DESCRIPTION: This project will use data from an ongoing multi-community trial to identify individual and community level risk factors that are associated with nasopharyngeal colonization with Streptococcus pneumoniae in young children. We will conduct a cross-sectional study to evaluate how community-level characteristics, in addition to individual risk factors, aid in describing the likelihood of colonization with resistant strains. We will further use the identified risk factors in a mathematical transmission model to predict proportional resistance in a community and evaluate changes in proportional resistance based upon alteration of modifiable risk factors. Our specific aims include: 1) Determination of individual and community-level risk factors associated with nasopharyngeal colonization with Streptococcus pneumoniae in young children, regardless of susceptibility pattern. 2) Determination of individual and community-level risk factors associated with nasopharyngeal colonization with penicillin-resistant Streptococcus pneumoniae in young children. 3) Development of a mathematical transmission model that can predict the rate of change in pneumococcal prevalence based upon identified individual and community-level risk factors, and alteration of these risk factors within the transmission model to predict their effects on future pneumococcal prevalence.